Intra-city buses have included wheelchair lifts for transporting persons of limited mobility in and out of the vehicles. Typically, a prior art wheelchair lift included a mechanically driven platform to raise and lower a passenger between loading from outside of the vehicle at ground level and entry into the vehicle at a vehicle floor level. For example, wheelchair lifts of the type installed in the stairwell of transit vehicles, such as intra-city buses, have been used for some time. One type of prior art wheelchair lift, commonly referred to as a "step lift" was disclosed in U.S. Pat. No. 4,466,771 to Thorley et al. The step lift in Thorley et al. was designed to be installed in the stairwell of a transit vehicle, and included hinged panels that were movable between a step configuration and a platform configuration. In the step configuration, the hinged panels formed steps for use by passengers to board and exit the vehicle. In the platform configuration, the hinged panels formed a horizontal platform used to raise and lower a wheelchair passenger between a vehicle floor-level position and a ground-level position.
Municipalities recently began using "low floor buses." In this style of bus, a passenger entered the bus at a level that was above ground by a sufficient amount so that the chassis had proper ground clearance. The floor of the bus throughout the vehicle was substantially at this level. It was believed that such buses were more stable in operation, and permitted simpler egress and ingress of passengers.
A problem encountered with the low floor buses was that wheelchair lifts such as were disclosed in Thorley et al. could not be installed in the buses because there was not a stairwell. Moreover, the low floor buses lacked sufficient under-chassis space to mount the complex lifting mechanisms for a wheelchair lift. Therefore, other systems had to be developed to accommodate wheelchair users and other passengers of limited mobility. To address these concerns, some manufacturers developed ramp assemblies for providing limited mobility passengers access into and out of the low floor buses. The ramp assemblies were structures that selectively provided a ramp platform that extended between the outside ground and the floor of a vehicle such as an intra-city bus to provide access into and out of the vehicle.
Prior art ramp assemblies typically stowed the ramp platform under the vehicles when not in use, and deployed the ramp platform when it was necessary to provide passenger access. When the ramp platform was deployed, the two ends were positioned at different heights, creating a slope upward from the ground to the bus floor. An example of a ramp assembly for use in a low floor bus was disclosed in U.S. Pat. No. 5,636,399 to Tremblay et al. A similar ramp assembly for use in a van was disclosed in U.S. Pat. No. 5,393,192 to Hall et al.
One of the problems found in designing prior art ramp assemblies for low floor vehicles was the limited amount of space allotted for the ramp platform and its reciprocating mechanism, including the motor and necessary drive mechanism. Because the low floor buses lacked a stairwell and a raised floor under which the ramp assembly could be mounted, the designer was forced to minimize size in all dimensions to prevent loss of ground clearance or interference with other under-chassis structures. Tremblay et al. and Hall et al. addressed this problem by providing a compact ramp assembly. However, while the ramp assemblies disclosed in Tremblay et al. and Hall et al. were relatively small, the motors used for the ramps were mounted behind or underneath the frame for the ramp assembly, requiring additional installation area underneath the vehicle. There exists a need for a more efficient manner of mounting a motor for a ramp assembly.
Another problem with the prior art ramp assemblies was that the ramp platform was stowed several inches below the floor level and, to reach the deployed position, had to be raised to extend between the floor and the ground. Alternatively, some form of transition between the ramp in the deployed position and the floor had to be provided. Tremblay et al. addressed this problem by providing a hinged panel that formed a transition between the floor and the ramp platform. Hall et al., on the other hand, provided a complex tilting mechanism utilizing a reciprocating motor to lift the trailing end of the ramp to floor level. There is a need for a less complex mechanism for providing a transition between the floor and a ramp platform.
Another problem with prior art ramp assemblies is that, if power was cut to the reciprocating mechanism for the ramp platform, the ramp platform may be stuck in a deployed position. In such case, the driver of the bus would have to wait for maintenance crews to repair, or at least stow, the ramp platform. There is a need for a more simple way of retracting a ramp platform when the reciprocating mechanism for the ramp platform is inoperable.